Keypads and key switches

ABSTRACT

A keypad with both elevated and non-elevated key regions, and key switches disposed beneath both types of key regions. The non-elevated key regions each provide corresponding character output based on an operation algorithm that considers activation of at least one adjacent elevated key region as well as activation of the switch below the non-elevated key region. The keypad includes a keymat that is rigidly held at its perimeter in a stretched condition across a switch substrate. The key switches include metal snap domes that have an elevated central region forming a downwardly facing cavity defined at its edge by a ridge disposed above the switch contacts that electrically engages multiple switch contacts in an annular contact zone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application PCT/US03/16490, filed May 23,2003, and also claims priority through the PCT application under 35U.S.C. §119(e) from U.S. provisional patent application Nos. 60/382,906filed May 23, 2002, 60/419,843 filed Oct. 21, 2002, 60/431,796 filedDec. 9, 2002, and 60/444,227 filed Feb. 3, 2003. All of these priorityapplications are hereby incorporated by reference, in their entirety.

TECHNICAL FIELD

This invention relates to keypads, and to key switches for keypads andkeyboards.

BACKGROUND

The miniaturization of electronic products is one of the primary tenetsof technologic advance. Competitive advantage and the success of aproduct line largely hinges on the ability of a company to successfullyprovide products that are both increasingly functional and increasinglyportable. As technology advances, it becomes increasingly possible tominiaturize electronic circuitry below human scale, with the resultbeing that the interface alone (e.g., screens, keypads, cursor controldevices) come to define the size of portable products. Therefore, theergonomic quality and size of input devices (such as keypads) continueto have a growing significance to product acceptance and success.

One type of keypad or keyboard that provides a particularlyspace-efficient input means are Independent And Combination Key (IACK)keypads, having arrays of effectively lower, concave combination keyregions interspersed among an array of effectively elevated, convexindependent key regions. IACK keypads have both independent andcombination key regions, typically arranged in alternating rows andcolumns. Independent key regions of my prior IACK keypads were elementsof the keypad that, when pressed independent of adjacent keys, producedan associated output. By contrast, the combination key regions of myprior IACK keypads were keypad elements with adjacent independent keys(such as at diagonally-oriented corners of the combination key region)with no corresponding key switches underlying the keymat. Outputcorresponding to the combination key region was produced by pressing twoor more adjacent elevated key regions in combination.

Other improvements leading to reliable operation of increasinglyminiaturized keypads are desired, even in keypads that don't require theoutput of some key regions to be produced by activating combinations ofswitches corresponding to other key regions. For example, improvementsare sought in the construction of key switches that can reliably andnear-simultaneously close multiple electrical connections with a single,defined tactile feedback event. There is a class of keyboards andkeypads, including LACK keypads, that require multiple key switchcontacts to be made simultaneously. Snap domes (made from materials suchas metal and plastic) that operate in a buckling mode provide a highquality of tactile feedback. It is extremely difficult, however, to makereliable momentary connection to more than one key switch contact at atime.

SUMMARY

According to one aspect of the invention, an improvement is provided forkeypads having a matrix of key regions including both an array ofelevated key regions each providing a corresponding character outputwhen actuated, and key regions interspersed between the elevated keyregions and providing character output based at least in part on anoperation algorithm that includes activation of at least one adjacentelevated key region. The improvement features corresponding,independently actuatable key switches disposed below the interspersedkey regions, the operation algorithm also including actuation of theassociated switches below the interspersed key regions.

Preferably, adjacent elevated key regions have an on-center distance ofless than about half the width of the adult human finger.

In some cases, corresponding tactile feedback elements underlie eachelevated key region and each interspersed key region.

In some implementations the operation algorithm, in response to sensinga combined switch actuation including any switch underlying an elevatedkey region and a switch underlying an interspersed key region, producesan output corresponding to the interspersed key region.

In some instances the operation algorithm, in response to sensing acombined switch actuation including a switch underlying an interspersedkey region and any switch underlying an elevated key region immediatelyadjacent that interspersed key region, produces an output correspondingto the interspersed key region.

In some situations, each switch disposed below an interspersed keyregion is directly connected to a switch disposed below anotherinterspersed key region on one side, and to a switch disposed below anelevated key region on another side.

The interspersed key regions, in at least some embodiments, have exposedsurfaces that are convex. In some other cases, they are substantiallyflat.

In some cases, the elevated key regions each include an elevated ridgedefining a top surface and each interspersed key region is immediatelyadjacent a plurality of the elevated key regions.

In some embodiments, the keypad includes a printed circuit board withtraces electrically connecting each of at least some switches underlyingelevated key regions with a switch underlying a corresponding one of theinterspersed key regions.

In some cases, the keypad has a printed circuit board with fourelectrical trace extensions extending to beneath each of theinterspersed key regions, to form switch contacts. For example, two ofthe trace extensions under each interspersed key region may connect to atactile dome, and the other two trace extensions connect to exposedtraces that are momentarily placed into electrical contact when thatinterspersed key region is actuated.

In some preferred constructions, each switch disposed below aninterspersed key region is actuated by electrical traces of a printedcircuit board contacting a discontinuity in an inner surface of a metalsnap dome. Preferably, the traces contacted by the snap dome surfacediscontinuity form three discrete contacts spaced about a circularcontact zone beneath the snap dome. The traces may be pie-shaped beneaththe snap dome, for example.

In some cases, the switches disposed below the interspersed key regionseach includes a tactile feedback element and a carbon ring. In suchcases, the tactile feedback elements may be electrically passive. Theswitches disposed below the interspersed key regions may each beconnected to three signal traces, forming a single access to the switchfrom one side of the matrix, and two access points from another side ofthe matrix.

In some keypads, either the elevated or interspersed key regions arerespective areas of a molded plastic keymat that flexes during keyactuation. In some cases, key regions that are not respective areas ofthe molded plastic keymat are exposed through respective, spaced apartholes in the keymat. In some cases, snap dome actuators are molded toextend from a lower surface of the keymat. The keymat may also be moldedintegrally with a product housing.

In some other cases, the key regions are upper surfaces of keys securedto a sheet held in a stretched condition above an array of key switches.The stretched sheet may comprise a sheet of elastomeric resin, forexample. Preferably, the elastomeric sheet is held in a stretchedcondition of at least 20 percent in at least one direction. In someinstances, the stretched sheet comprises a plastic sheet molded to havea resiliently distendable region, such as a pleat extending out of aprincipal plane of the sheet.

According to another aspect of the invention, an improvement is providedfor a keypad comprising a keymat and a switch substrate underlying thekeymat, the keymat having an exposed upper surface forming separateelevated key regions that, when pressed independent of adjacent keyregions, produces an associated output, the keymat also defining otherkey regions interspersed between adjacent elevated key regions andlabeled to indicate other associated outputs. The improvement featuresthat the keymat is rigidly held at its perimeter in a stretchedcondition across the switch substrate.

In some embodiments, the elevated key regions are upper surfaces ofrigid keys secured to an elastomeric sheet.

The elastomeric sheet is preferably held in a stretched condition of atleast 20 percent in a given direction, or held stretched in each of twoorthogonal directions.

Some examples feature a keymat with a plastic sheet molded to have aresiliently distendable region, such as a pleat extending out of aprincipal plane of the sheet.

In some embodiments, the keymat defines peripheral holes that, with thekeymat stretched, receive pins of a rigid keypad housing.

According to a third inventive aspect, an electrical key switch includesa printed circuit board with at least two switch contacts that arenormally electrically isolated from each other, and a metal snap domedisposed above the printed circuit board. The dome has an elevatedcentral region forming a downwardly facing cavity defined at its edge bya ridge disposed above the switch contacts, such that when the snap domeis actuated the ridge about the central region engages the printedcircuit board in an annular contact zone across the switch contacts,making electrical contact between the snap dome and the switch contacts.

In some embodiments, the snap dome has an outer edge disposed againstand in electrical contact with a reference trace on the printed circuitboard.

Preferably, the annular contact zone is about one-third of a nominaldiameter of the metal dome.

The switch contacts, in one illustrated embodiment, are wedge-shaped.Preferably each switch contact extends across about 20 degrees of thecircumference of the contact zone.

The switch contacts are preferably disposed approximately equidistantfrom each other about the contact zone.

In some cases the ridge forms a continuous ring. In some other cases theridge comprises a ring of spaced ridges or ridge segments.

In some applications the snap dome overlays three spaced apart switchcontacts.

In some cases, the switch contacts are sufficiently thick that thedeflected snap dome contacts all underlying switch contacts beforecontacting any other surface of the PCB, and preferably the snap dome issufficiently thin and the switch contacts sufficiently spaced apartthat, with the deflected dome in contact with all of the underlyingswitch contacts, the dome can deflect further toward the PCB betweenadjacent switch contacts.

In another inventive improvement to a keypad comprising a keymat and aswitch substrate underlying the keymat, the keymat having an exposedupper surface forming separate elevated key regions that, when pressedindependent of adjacent key regions, produces an associated output, thekeymat also defining other key regions interspersed between adjacentelevated key regions, the switch substrate includes both switchesunderlying associated and elevated key regions and switches directlyunderlying corresponding ones of the interspersed regions.

According to another improvement for keypads having a matrix of keyregions including both an array of elevated key regions each providing acorresponding character output when actuated, and key regionsinterspersed between the elevated key regions and providing characteroutput based at least in part on an operation algorithm that includesactivation of at least one adjacent elevated key region, theinterspersed key regions have a notably convex upper surface.

Placing multiple switches under a finger is at odds with basic tenets ofsound ergonomic design: that of providing one distinct tactile feedbackfor each input received. Some of my early attempts to provide ahigh-level (metal dome) tactile feedback yielded unacceptablecombination key reliability and multiple “clicks” per input. Ultimately,the solution presented by some of the embodiments disclosed hereinrequired multiple concurrent changes, including adding an additionaltactile feedback (as a means to solve the problem that there was alreadytoo much feedback), adding a submatrix within the PCB matrix (which,without some of the improvements disclosed herein) would have theundesirable effect of increasing the number of lines to a centralprocessor, and, in some respects, abandoning the early IACK concept (ofhaving opposing diagonals of elevated keys producing an outputassociated with a central combination key region) in favor of ahierarchical approach between non-elevated and elevated keys, in whichthe non-elevated keys became dominant. Furthermore, the improved keymatstructures improves the ability of a generic finger to actuate bothindependent and combination keys reliably.

A keypad structure is provided that employs the relative height andrelative strength of a single dome structure with respect to foursurrounding it, and a relatively weak deflection force within the keymatitself. This approach is particularly advantageous in combination withconvex, non-elevated keys.

The reliability of making multiple switch contacts with a single metaldome is enhanced by narrowing the traces that contact the discontinuityand thickening the metal of the traces such that portions of thediscontinuity locate between the three discrete contacts may materiallydeflect toward a printed circuit board as the discontinuity is incontact with the three discrete contacts. The reliability of makingmultiple contacts at once is particularly enhanced, especially if thesnap dome and traces only contact each other at the “triple point”, orlocations that divide the diameter approximately into thirds.

Material property differences between an elastomeric keypad web held ina plastic housing can result in a loss of contact with the snap domesunder extreme temperature variations. In order to maintain contactbetween the keymat actuators and domes without needing to use anadhesive (which adds service and manufacturing concerns) it is desirableto assemble the keymat into a pre-stressed or stretched state.

Some aspects of the invention can enable a miniaturized keypad thatstill has a well-defined, subjectively good tactile feedback for eachkey entry, whether of an elevated or non-elevated key region. Otherfeatures disclosed and claimed herein can improve the durability ofkeymats, such as by providing a hard plastic keypad that allows thekeypad to be integrated with the housing, minimizing the number ofexposed edges in a keypad tiling, etc. Still other improvements increasethe useful life and operability of flexible keymats. The improved domeswitch construction disclosed herein can produce reliable,near-simultaneous connections across two or more contact paths with asingle tactile feedback to the user.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Some of theseembodiments are described with respect to improvements to IACK keypads,or to keypads having key regions whose output is determined only by thecombined states of switches associated with adjacent, elevated keyregions. However, it will be understood that several aspects of theinvention are not limited to such types of keypads, and that othersdistinguish such operational algorithms. Other features, objects, andadvantages of the invention will be apparent from the description anddrawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a first printed circuit board (PCB) for a keypad, with someswitches including both exposed carbon and metal dome switch plates.

FIG. 2 shows a cross section of a keypad with elevated and interspersedkey regions.

FIGS. 3 and 4 illustrate the actuation of a combination key region andan independent key region, respectively, of a thermoformed LACK keymat.

FIG. 5 shows narrow actuation posts molded in to a back-filledelastomer.

FIGS. 6 and 7 show operational algorithms for a keypad.

FIGS. 8 and 9 show circuit board layouts useful with the algorithms ofFIGS. 6 and 7.

FIG. 10 shows a finger pressing on an elevated key region.

FIG. 11 shows a finger pressing on a convex, non-elevated key region.

FIG. 12 shows a finger pressing on a flat, non-elevated key region.

FIG. 13 shows a finger pressing on an elevated key region with a raisededge.

FIG. 14 shows an elastic keymat disassembled from its housing.

FIG. 15 shows the keypad of FIG. 14 as assembled FIG. 16 shows a keypadwith a keymat molded with a flexure points.

FIG. 17 shows a keymat with independent key regions defined on a rigidstructure.

FIG. 18 is a cross-sectional view, taken along line 18-18 of FIG. 17.

FIG. 19 shows a keymat with combination key regions defined on a rigidstructure.

FIG. 20 is a cross-sectional view, taken along line 20-20 of FIG. 19.

FIG. 21 is a cross-sectional view taken through a metal dome designed tocontact multiple switch elements at once.

FIG. 22 shows the PCB traces underlying the dome of FIG. 21.

FIG. 23 shows a discontinuous ring element on the underside of a metaldome.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows switches 21 to accommodate traditional snap domes 12 (FIG.3) made of metal or plastic providing a momentary connection between twolines located at one of the intersections of drive lines 24 (shownvertical) and sense lines 26 (shown horizontal), under the independentkeys 11 of an IACK keypad having an array of independent key regions 11interspersed between combination key regions 22 (see also FIGS. 3, 10).The base of snap dome 12 (preferably made of metal) rests on a printedconductive base 29 in electrical contact with the drive lines 24 aboveit, and the center of switch 21 is in electrical continuity with thesense line 26 to its right. The result is that actuation of associatedsnap dome 12 is the electrical equivalent of actuating the switch underthe independent key 11 located upwards and to the right of the intendedcombination key 22. Also shown is one auxiliary contact 20 in electricalcontinuity with the drive line 24 below it, and one auxiliary contact 20in electrical continuity with the sense line 26 to its left. A tapelayer covers the snap domes 12, preventing contact to auxiliaryconductor 18 (FIG. 3), and also has cut outs corresponding withauxiliary contacts 20 that allow contact between the auxiliaryconductors and the PCB. The result is that actuation of associated snapdome 12 is the electrical equivalent of actuating the switch under theindependent key 11 located downwards and to the left of the intendedcombination key 22. The simultaneous actuation of these two independentkeys 11 (located diagonally opposite from each other across acombination key 22) acts as an indication to the controller that theintent is to actuate the central combination key.

FIG. 2 shows drive lines 24 electrically isolated from sense lines 26,although electrical connectivity between them can be made at eachindependent intersection 14, corresponding to the location of anindependent key region 11. As in some earlier IACK keypads, the softwareof the system registers a combination key input as a result ofactivation of at least two diagonally adjacent (i.e. opposite adjacent)independent key regions 11. For example, activating both “E” and “L”, or“F” and “K”, is registered by the system as an intention to enter thenumber “3”. In this matrix, however, trace extensions 50 extend fromeach of the four trace segments that bound each combination key region22, to almost contact each other at each combination intersection 15.Trace extensions 50 extend in each combination key region 22 to within acontact region 141. Extensions 50 may be made of as conductive ink whichmay be selectively doped or otherwise varied to provide a uniqueresistance at each intersection during contact, such that the identityof the intersection under contact can be verified by sensing traceresistances.

Actuation of a combination key 22 directly above a combinationintersection 15 closes contact between the four adjacent ends of thetrace extensions 50 at that intersection 15, thereby connecting theadjacent pairs of drive lines 24 and sense lines 26 and creating theelectrical equivalent of actuating all four surrounding independentintersections 14. Examples of switch constructions for connecting allfour trace extensions 50 of a given combination intersection 15 areshown in FIGS. 1 and 21-23.

FIGS. 3-4 illustrate the operation of an IACK keymat 30 a having a thinsheet 70 formed into the undulating surface contour of the exposed keyregions, including elements for independent keys 11 and combination keys22. The sheet 70 may be made of relatively hard and stiff material, suchas polycarbonate or polyester, and formed with a process such asthermoforming. A sheet thickness of 0.002 to 0.005 inch is preferred,for example. Below each independent key region 11 is an actuator 36 ofanother material, formed in place such as by injection molding.Actuators 36 are disposed directly above respective, high-feedback n,such as metal or polyester domes. Likewise, there is an actuator 36 andhigh-feedback snap dome 12 below each combination key region 22.

As shown, there is a difference in the spacing between the lowersurfaces of actuators 36 and their associated snap domes 12. The area ofcontact between sheet 70 and the actuators 36 of the independent keys 11is limited to the portion of the independent key 11 that will not deformduring use, predominantly the flat area at the top that is contacted bya finger 55 during activation of the independent key 11. The object isto transmit force to the tactile feedback element 12 while minimizingthe rigidity of the sloped sides of the independent keys 11. Thestructure or structures that transmit force between sheet 70 and tactilefeedback elements (snap domes) 12 need not be attached to sheet 70. Atrest the actuators 36 located below independent key regions 11 areseparated from their associated tactile elements by a distance “d” atleast slightly greater than the stroke length of the tactile elements.In this illustrated embodiment, the heights and stroke lengths of allsnap domes 12 are the same. Tactile feedback (specifically one distinctsensory feedback for one input sensed) is an extremely important aspectof any keypad, and in opposition to the inherent nature of a technologythat places a plurality of tactile elements directly beneath a user'sfinger, such as IACK. This structure provides a single, well-definedtactile feedback in an IACK keypad when either a combination key 22 oran independent key 11 is pressed.

As shown, independent key actuators 36 underlie only the uppermostplateau regions of the independent key regions 11, across which themajority of finger actuation force is applied. This leaves the slantedsides of the raised independent key regions 11 free to bend during keyactuation, as not constrained by actuators 36.

As a user's finger 55 presses to input the character printed oncombination key 22 (FIG. 3), some deformation occurs within sheet 70,but the primarily result is downward deflection of the adjacentindependent key regions 11 as the intended combination key region 22deflects downward. Notably, however, the snap dome 12 directly below thecombination key region 22 is tripped at a lower deflection distance thanthose of the adjacent independent key regions 11, as shown in FIG. 3.This provides a single and highly-defined tactile feedback (such as froma metal or poly dome) in response to actuating a combination key 22.

Conversely, as a user's finger 55 presses to actuate an independent keyregion 11 (FIG. 4), the snap dome 12 directly below that independent keyis tripped before any of the surrounding tactile elements is tripped. Aslong as the force required to deflect sheet 70 about the actuatedindependent key region 11 is less than the combined trip force of thesnap domes 12 located below the adjacent combination key regions 22, theselected independent key 11 will continue to advance to trip only itsassociated snap dome 12.

FIG. 5 shows keymat 30 b, a variation of the embodiment of FIG. 3, inwhich actuators 36 are formed of a rigid, optically transmissivematerial, and/or are cone-shaped for improved light transmission whileminimizing material compression. These may be formed with a two shotin-mold process, in which the elastomeric material forming web 97 isformed first and a second shot forms a higher durometer material of theactuators 36. Alternatively, concentrators 36 may be insert-molded in asofter elastomer. The upper surfaces of concentrators 36 may be shapedto form letters or other symbols identifying key regions.

FIG. 6 shows a decoding method that simplifies the software, reduces theprocessing steps necessary to operate an IACK keypad and enables highquality tactile feedback in an IACK keypad. In step 100 two classes ofkeys are created in software. These may be as simple as lists of the twotypes of keys (11 and 22), or also a list of one type of key and theremaining keys are (by default) of the second type. Independent keys 11are assigned to a secondary class and combination keys 22 are assignedto a dominant class. Notably, the relative locations of specificindependent 11 and combination keys 22 are not part of the decodingalgorithm, rather absolute location and class are used to define theintended output. Conversely, with some earlier IACK keypads, knowing therelative position of each key was fundamental to operation. In step 102,the system senses the user pressing a secondary key, such as independentkey 11. The system may post this key, or wait a designated delay period.In step 104 the user presses (and the system senses) another keyactuation before the secondary key is released. The software does notneed to analyze which diagonals are involved and perform a correlationbetween the selected diagonals and the combination key between them, asany key of the dominant class will supercede any key of the secondaryclass. Referring briefly to FIG. 9, in some prior art IACK keypads,activation of the ‘A’ key would have required activation of elevated keyregions 1 and 6, or 2 and 5. However, in this algorithm any of numerickeys 1 through 12, in combination with ‘A’ will yield an ‘A’ output, aswill key ‘A’ by itself. The locations of the independent keys areimmaterial. In step 106 the system abandons the secondary key for theprimary key. This algorithm may not be as useful with some prior artIACK keypad structures having a high-quality tactile feedback and thatoperated on the principle of opposite adjacent independent keys 11indicating intent to actuate a combination key 22. In those cases,operation of a combination key necessitated the actuation of at leasttwo snap domes 12 (in keypads with snap domes) because the independentkeys were spaced apart less than half of an adult finger width apart foroverall size reduction. This algorithm (or that of FIG. 7) used incombination with the convex combination key structure of FIG. 11 allowsfor individual high-quality tactile feedback in IACK keypads.

FIG. 7 shows another decoding method that simplifies the software,reduces the processing steps necessary to operate an IACK keypad andenables high quality tactile feedback in an IACK keypad. This method(like that of FIG. 6) is suitable for use with printed circuit boardlayouts as shown in FIGS. 8 and 9. In step 110, two classes of keys areidentified, analogous to step 100 in FIG. 29. However, in step 112,additional lists are created in which each dominant key is associatedwith the adjacent secondary keys. Referencing FIG. 9, ‘A’ is associatedwith 1, 2, 5 and 6; ‘B’ with 2, 3, 6 and 7; ‘C’ with 3, 4, 7 and 8; ‘D’with 5, 6, 9 and 10′; ‘E’ with 6, 7, 10 and 11; and ‘F’ with 7, 8, 11and 12. Note that the same result may be achieved by creating a singleset of lists in which a predefined element is of a particular class,such as: ‘A,1,2,5,6’; ‘B,2,3,6,7’; ‘C, 3, 4, 7, 8’; ‘D, 5, 6, 9, 10’;‘E, 6, 7, 10, 11’; and ‘F, 7, 8, 11, 12’ in which a particular characterof each list (in this case the first character) is the dominant key. Theother characters, identifying physically adjacent keys, may be listed ina random order, as location with respect to the dominant (combination22) key is immaterial. In step 115 a plurality of keys are pressed bythe user and sensed by the system. In step 117 the system references theclassifications and prioritizations made in steps 110 and 112. If one ormore secondary keys are sensed during the initial instant of an inputstroke, and the system later senses a dominant key prior to thedeactivation of all the secondary keys, the system will abandon thesecondary keys in favor of the dominant key, step 106. As with themethod of FIG. 6, output is not based exclusively on combinations ofopposite-adjacent keys, as with many prior IACK keypads. This method incombination with the PCB layout of FIG. 8 also allows successfuldifferentiation between independent, combination and ambiguous keygroupings in a single cycle by driving adjacent drive linessimultaneously. Specifically, in some prior art IACK keypads it waspossible to drive adjacent lines simultaneously and thereby determine acombination key in a single step, an approach that can yield ambiguousresults if two adjacent horizontal or two adjacent vertical keys arepressed. This ambiguity required a second cycle to determine the truestate of the switch matrix. This problem is now solved in that adjacentdrive lines may be pulsed simultaneously to provide non-ambiguousinformation of the matrix and accurately determining both independentand valid combination key combinations in a single cycle. This methodalso works for keypads in which keys are independently addressable, suchas keypads in which each switch as an associated diode.

FIG. 8 shows a hardware configuration for implementing the methods ofFIGS. 6 and 7. Sense lines 26 have been added to measure output fromcombination keys 22. Switches 21 that are dedicated to combination key22 input are driven through the drive lines 24 of the independent keys11. The input is provided to combination keys 22 by bridge 31 that tapsa signal from the drive line 24 of independent keys 11. Sense lines 26lead to processor 151. An electrical word on the drive lines 24 can beread on the sense lines 26 to identify any combination key 22 orindependent key 11 switches. This information is used preferably withthe methods of FIGS. 6 and 7.

FIG. 9 shows another PCB design useful for implementing the methods ofFIGS. 6 and 7. In this case, switches of combination key 22 are feddirectly by drive lines 24, labeled as DR2, DR4, and DR6.

Referring next to FIG. 10, the force applied by the finger 55 isconcentrated at its center region 34, at the peak of the curvature andcentered under the bone. The force is transmitted through center region34 and the outer portions of finger 55 conform around elevated keyregion 11. Local depression 136 is formed between the independent key 11on one side and a convex surface 38 of combination key region 22.Depressed region 136 provides a tactile distinction between theindependent keys 11 and combination keys 22.

FIG. 11 shows a finger 55 pressing against combination key 22.Combination key 22 is crowned, with a convex shape 38, presenting anelevated surface to meet the center region 34, but not elevated ascompared to the independent key regions 11, which are at leasteffectively elevated over the combination key regions 22 in that afleshy finger 55 will advance farther into the keypad to activate acombination key region 22 as placed in FIG. 11, than the same fingerwould to activate an adjacent independent key region 11 when placed asin FIG. 10. Directly distal to center region 34 of combination key 22 isa depressed region 136 that dissociates force from the finger, with theresult of further concentrating the force in the center region 34 and tohelp avoid distributing force over a greater area and onto the adjacentindependent keys 11. This increases the force transmission throughconvex shape 38, and thereby allows the finger 55 to actuate combinationkey 22 (which includes a single and independently operable switch belowto provide a clearly defined tactile response) while reducing the chanceof actuating adjacent independent keys 11. The optimal relationshipbetween the diameter of the independent keys 11 and the diameter of thecombination keys 22 is approximately 1:2. However, the inadvertentactuation of one of more of the adjacent independent keys 11, such as byinaccurate finger placement or a large finger, may be accommodated bythe electronics of FIG. 8 or 9 and the algorithm of FIG. 6 or 7. Tactilefeedback (preferably, one distinct sensory feedback for one inputsensed) is an important aspect of any keypad. These structures provide asingle, well-defined tactile feedback in an IACK keypad when either acombination key 22 or an independent key 11 is pressed.

FIG. 12 shows a finger pressing against a combination key region 22 withan effectively flat shape 140. Again, a single and independentlyoperable switch below the combination key region provides a clearlydefined tactile response.

FIG. 13 shows a finger pressing against an elevated key region 11 of akeypad in which the keypad surface is basically planar, with theindependent keys 11 identified by a tactile element 142 such as a ringor edge definition and combination key 22 is concave.

FIG. 14 shows a keypad disassembled from the housing 90 of theassociated electronic device. Separate combination keys 22 andindependent keys 11 are adhered to an elastomeric sheet 41. In order toincrease the reliability of consistent mechanical contact between theactuators 36 and snap domes 12, the elastomeric sheet 41 is manufacturedundersized with respect to the restraint elements 143, so thatelastomeric sheet 41 is placed in tension when assembled, as shown inFIG. 15. In other words, the elastomeric sheet is stretched (i.e.,placed in tension) to fit onto the restraint elements. That is to saythat the distance across the housing between the restraint elements 143is greater than the distance between the corresponding location features49 in the sheet 41. The keys in the center (such as the center one here)are located as they will be after assembly, however in one embodiment;keys increasingly near the periphery are adhered to the sheet 41 at anincreasingly proximal location to their post-manufactured position, sothat upon assembly (and stretching of the sheet 41), the keys arecorrectly positioned. Dimension “x” shows the gap between adjacent keysprior to assembly. Likewise, in one embodiment, the position of eitherthe actuators 36, or the metal domes 12 and the dome's switches 48 aredisplaced (misaligned) relative to the non-assembled sheet 41, such thatthe actuator 36, metal dome 12 and dome switches 48 printed on PCB 23align only after assembly (as shown in FIG. 15).

Referring to FIG. 15, when the keypad is assembled the gap betweenadjacent keys is denoted as “y”. At the edge of a typical keypad, (thekeys most effected) the difference between “x” and “y” is over 20percent, typically on the order of 20 to 80 percent. After assembly thekeys and actuators 36 align with the switches 48. The keypad is designedundersized to the opening in the housing 90. Alternatively, the keystructures may be secured to the elastomeric sheet with the sheet in itsstretched state, to control inter-key gap distances. The elastomericsheet 41 a of the keypad of FIG. 16 is molded to have a pleat 47 orother resilient formation that acts as a means to maintain tension inthe elastomeric sheet over a wider range of temperatures for a giventension. The distance between the restraint elements 143 is larger thanthe distance between the corresponding location features 49 in the sheet41, such that in the assembled keypad, flexure 47 is somewhat distendedfrom its molded state.

FIG. 17 shows an IACK keypad 10 including a plastic (predominantlyrigid) web, approximately 0.5 to 1.0 millimeter thick, forming acontinuous surface over the area of the keypad, with holes through whichthe combination keys 22 are exposed. The dashed area designates theextent of the web 40. Because the web 40 is a plastic material it can bemade of the same material as the housing 90 of the product itself, andfurthermore, can be made continuous with the housing 90 of the product.This can provide a significant advantage in design flexibility,aesthetics (by virtue of being the same material the problems of colormatching dissimilar material, potentially manufactured in differentfacilities, is eliminated), durability, and cost. No tilings are used,eliminating edges which could catch on a fibrous material, such as asweater. Independent keys 11 are defined by local elevations of thematerial of the web 40, and are activated by flexure of the hardplastic. The combination keys 22 are discrete plastic (predominantlyrigid) keys located in the holes in the web 40. The result is apredominantly rigid keypad with sufficient flexure to allow tactilefeedback to be felt by the user. Additional troughs may be provided inthe backside of the web to increase its flexibility, preferably orientedalong a common direction allows for the flow of fluid plastic during themanufacturing process. The transition region between the housing andkeymat may be thinned, or formed of a lower durometer material, such aspolyurethane, to allow for additional compliance at the edge of thekeymat. The relatively non-motile portions (in this case the independentkeys 11 and web 40) can be referred to jointly as the face plate of thekeypad.

Referring also to FIG. 18, combination keys 22 include a slight (convex)protrusion, or small hill, although notably shorter than the height ofthe independent keys 11. The independent keys 11 are taller than thecombination keys 22 by approximately 0.25 to 0.75 millimeter. Theoverall heights of the keys, as measured from the lowest surface of theactuator 36 to the highest surface above it, is such that the bulk ofthe force profile (center region 34) provided by the curvature of auser's finger (higher in the center and progressively less toward theedges) fits within the region of the combination key 22, including thestate after the snap dome 12 has been actuated. In another embodiment,independent keys 11 and combination keys 22 are nearly the same height.The discontinuous keys are held to the keypad 10 by an elastomeric sheet41. Although web 40 is rigid, the overall structure can displacerelative to PCB 23 and the web 40 can displace relative to thecombination keys 22. This flexure/displacement allows operation of IACKkeypads with a rigid plastic face.

FIG. 19 shows an example in which the combination keys 22 are integrallymolded with the web 40, and independent keys 11 are discontinuous. Therelatively non-motile portions (in this case the combination keys 22 andweb 40) can be referred to jointly as the face plate of the keypad 10.While pressing combination keys 22, the face plate deflects.

Referring also to FIG. 20, the extent of the oval of the combination key22, along its major axis, is labeled as “W”. In this embodiment, thecontiguous extra width of the web 40 (beyond W) provides an effectiveincrease in the size of the combination key 22 relative to theembodiment of FIGS. 17 and 18, thereby assisting the designer to keepthe bulk of the force profile of the users finger away from actuatingthe hill keys. Note also that accidental actuation of hill keys 11 isacceptable, as the only detriment is additional tactile feedback. Theextra signal provided to the system does not cause a problem. Althoughweb 40 is rigid, the overall structure can displace relative to PCB 23and the web 40 can displace relative to the independent keys 11. Thisflexure/displacement allows operation of IACK keypads with a rigidplastic face plate. The discontinuous keys are held to the keypad 10 byan elastomeric sheet 41. It is also possible to implement theembodiments of FIGS. 18 and 20 in the same product by providingindependent motility in both independent keys 11 and combination key 22as long as web 40 is allowed low-force flexure at least as long as thestroke of key actuation.

Referring next to FIGS. 21 and 22, a metal snap dome 12 has an elevatedcentral region 212 forming a downwardly facing cavity 13 defined at itsedge by a geometric discontinuity 214 such as a ridge as shown. Thediscontinuity 214 is disposed above at least two switch contacts 16 thatare normally electrically isolated from each other, disposed on printedcircuit board 23. Metal snap dome 12 includes edge 118, which rests uponanother electrically distinct switch element, signal reference 224.Actuator 36 is located to apply force to, and thereby displace, elevatedcentral region 212. Note that forces applied by the actuator 36 are nottransmitted to the PCB 23 downward (below the center of the actuator20), but by material located off-center, in this case the underside ofdiscontinuity 214 located radially outward from the center 17 of theactuator. The result is that the bulk of the force applied by theactuator 36 is not applied in a point, but distributed over a line, inthis case a line curved to form a circular contact zone 230. Contactzone 230 is approximately {fraction (1/3)} the nominal diameter of themetal dome 12, creating “third” points, or contact points (in thecontact zone 230) approximately equidistance between edges 118 and eachother. Therefore as one side of discontinuity 214 touches a first switchelement 16 a torque will be placed upon that contact point, acting toforce the other side of discontinuity 214 into contact with a secondswitch element 16. The objective is to reliably connect two or moreseparate electrical lines to a common signal reference 224. Thediscontinuity 214 may be in the form of a downward ring-likeindentation, such that the elevated central region 212 is elevatedrelative to the lower edge of the discontinuity 214, but not distinctlythe rest of the snap dome 12.

As shown in FIG. 22, along the contact zone 230 the dome contacts threeswitch elements 16. Signal reference 224 acts as the fourth element.Vias 32 connect switch elements 16 to traces on lower layers of the PCB.Each switch element 16 extends over an angle α, in this example about 20degrees, equating to a total of approximately {fraction (1/6)} of thecircumference of contact zone 230 comprised of switch elements 16.Reducing the value of a furthers the objectives of the theory ofoperation explained in FIG. 21 by making contact with one or two switchelements 16 an unstable configuration. Therefore a force applied to thecenter axis 17 will apply an increased torque to assist withestablishing contact between the metal dome 10 and each switch element16, even if two contacts are already established. The instabilityprovided by contacting the snap dome 12, the torque provided bycontacting near the trip point and the narrowness of the traces, therebyincreasing local pressure, are among the envisioned potential advantagesof this approach. Note that three switch elements 16 are shown, two (andto a lesser extent four) switch elements 16 may also benefit from thisdesign. Discontinuity 214 may be formed as a ring of spaced ridgesegments, as shown in FIG. 23, with ridge lengths and gaps selected tofacilitate reliable contact with each switch element 16.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

1. A keypad comprising a matrix of key regions including an array ofelevated key regions each providing a corresponding character outputwhen actuated; and key regions interspersed between the elevated keyregions and providing character output based at least in part on anoperation algorithm that includes activation of at least one adjacentelevated key region; and corresponding, independently actuatable keyswitches disposed below the interspersed key regions, the operationalgorithm also including actuation of the associated switches below theinterspersed key regions.
 2. The keypad of claim 1 wherein adjacentelevated key regions have an on-center distance of less than about halfthe width of the adult human finger.
 3. The keypad of claim 1 comprisingcorresponding tactile feedback elements underlying each elevated keyregion and each interspersed key region.
 4. The keypad of claim 3wherein the operation algorithm, in response to sensing a combinedswitch actuation including any switch underlying an elevated key regionand a switch underlying an interspersed key region, produces an outputcorresponding to the interspersed key region.
 5. The keypad of claim 3wherein the operation algorithm, in response to sensing a combinedswitch actuation including a switch underlying an interspersed keyregion and any switch underlying an elevated key region immediatelyadjacent that interspersed key region, produces an output correspondingto the interspersed key region.
 6. The keypad of claim 1 wherein eachswitch disposed below an interspersed key region is directly connectedto a switch disposed below another interspersed key region, and to aswitch disposed below an elevated key region.
 7. The keypad of claim 1wherein the interspersed key regions have exposed surfaces that areconvex.
 8. The keypad of claim 1 wherein the interspersed key regionshave exposed surfaces that are substantially flat.
 9. The keypad ofclaim 1 wherein the elevated key regions each include an elevated ridgedefining a top surface.
 10. The keypad of claim 1 wherein eachinterspersed key region is immediately adjacent a plurality of theelevated key regions.
 11. The keypad of claim 1 including a printedcircuit board with traces electrically connecting each of at least someswitches underlying elevated key regions with a switch underlying acorresponding one of the interspersed key regions.
 12. The keypad ofclaim 1 including a printed circuit board with four electrical traceextensions extending to beneath each of the interspersed key regions, toform switch contacts.
 13. The keypad of claim 12 wherein two of thetrace extensions under each interspersed key region connect to a tactiledome, and the other two trace extensions connect to exposed traces thatare momentarily placed into electrical contact when that interspersedkey region is actuated.
 14. The keypad of claim 1 wherein each switchdisposed below an interspersed key region is actuated by electricaltraces of a printed circuit board contacting a discontinuity in an innersurface of a metal snap dome.
 15. The keypad of claim 14 wherein thetraces contacted by the snap dome surface discontinuity form threediscrete contacts spaced about a circular contact zone beneath the snapdome.
 16. The keypad of claim 14 wherein the discontinuity is centrallylocated under the snap dome and is of a diameter about one third of anoverall diameter of the snap dome.
 17. The keypad of claim 1 wherein theswitches disposed below the interspersed key regions each includes atactile feedback element and a carbon ring.
 18. The keypad of claim 17wherein the tactile feedback elements are electrically passive.
 19. Thekeypad of claim 17 wherein the switches disposed below the interspersedkey regions are each connected to three signal traces, forming a singleaccess to the switch from one side of the matrix, and two access pointsfrom another side of the matrix.
 20. The keypad of claim 1 whereineither the elevated or interspersed key regions are respective areas ofa molded plastic keymat that flexes during key actuation.
 21. The keypadof claim 20 wherein key regions that are not respective areas of themolded plastic keymat are exposed through respective, spaced apart holesin the keymat.
 22. The keypad of claim 1 wherein the key regions areupper surfaces of keys secured to a sheet held in a stretched conditionabove an array of key switches.
 23. The keypad of claim 22 wherein thestretched sheet comprises a sheet of elastomeric resin.
 24. The keypadof claim 23 wherein the elastomeric sheet is held in a stretchedcondition of at least 20 percent in at least one direction.
 25. Thekeypad of claim 22 wherein the keymat comprises a plastic sheet moldedto have a resiliently distendable region.
 26. The keypad of claim 25wherein the resiliently distendable region comprises a pleat extendingout of a principal plane of the sheet.
 27. An electrical key switchcomprising a printed circuit board with multiple switch contacts and areference trace that are normally electrically isolated from each other;and a metal snap dome disposed above the printed circuit board andhaving an outer edge in electrical contact with the reference trace, thedome having an elevated central region forming a downwardly facingcavity defined at its edge by a ridge disposed above the switchcontacts, such that when the snap dome is actuated the ridge about thecentral region engages the printed circuit board in an annular contactzone across the switch contacts, making electrical contact between thesnap dome and the switch contacts to electrically connect the switchelement with the multiple switch contacts.
 28. The key switch of claim27 wherein the annular contact zone is about one-third of a nominaldiameter of the metal dome.
 29. The key switch of claim 27 wherein theswitch contacts are wedge-shaped.
 30. The key switch of claim 29 whereineach switch contact extends across about 20 degrees of the circumferenceof the contact zone.
 31. The key switch of claim 27 wherein the switchcontacts are disposed approximately equidistant from each other aboutthe contact zone.
 32. The key switch of claim 27 wherein the ridge formsa continuous ring.
 33. The key switch of claim 27 wherein the ridgecomprises a ring of spaced ridge segments.
 34. The key switch of claim27 wherein the snap dome overlays three spaced apart switch contacts.